This invention relates to an imaging system and more specifically to an electrophoretic imaging system.
In photoelectrophoretic imaging colored photosensitive particles are suspended in an insulating carrier liquid. This suspension is then placed between at least two electrodes subjected to a potential difference and exposed to a light image. Ordinarily, in carrying out the process the imaging suspension is placed on a transparent electrically conductive support in the form of a thin film and exposure is made through the transparent support while a second generally cylindrically shaped biased electrode is rolled across this suspension. The particles are believed to bear an initial charge once suspended in the liquid carrier which causes them to be attracted to the transparent base electrode and upon exposure, to change polarity by exchanging charge with the base electrode so that the exposed particles migrate to the second or imaging electrode thereby forming images on each of the electrodes, by particle subtraction, each image being complementary one to the other. The process may be used to produce both polychromatic and monochromatic images. In the latter instance a single color photoresponsive particle may be used in the suspension or a number of differently color photoresponsive particles may be used all of which will respond to the light to which the suspension is exposed. An extensive and detailed description of the photoelectrophoretic imaging techniques as generally referred to may be found in U.S. Pat. Nos. 3,383,993, 3,384,488, 3,384,565 and 3,384,566, and are hereby incorporated by reference.
In the case of the polychromatic imaging process the imaging suspension will contain a plurality of at least two differently colored finely divided particles in the carrier liquid each of said particles comprising an electrically photosensitive pigment whose principal light absorption band substantially coincides with its principal photosensitive response. Thus, the pigment represents both the primary electrically photosensitive ingredient and the primary colorant for the specific particle in suspension. The particles utilized in the polychromatic system preferably have intense pure colors and are highly photosensitive. When the suspension is exposed to a multicolored image, particles will migrate to one electrode in proportion to the intensity of the light which they absorb. Thus, upon exposure, particles selectively remain on one of the electrodes in image configuration with complementary particles migrating to the other of the electrodes in this system. For example, when a mixture comprising cyan, magenta and yellow particles is exposed to an image whereby yellow light impinged the imaging suspension, the cyan and magenta particles will migrate leaving behind an image made up of the yellow pigment particles. Similarly, when exposed to a multicolored image different colored particles absorb light of their complementary color in the appropriate image areas and migrate thereby leaving a full colored image behind corresponding to the original.
Although the above described imaging systems and processes have been found to be highly satisfactory one of the more troublesome problems encountered has to do with the elimination of background resulting from the migration and desposition of unwanted pigment particles. In the case of the monochrome imaging process the background deposition plays a more noticeable role in its effects upon the resulting image. In the polychrome process although not as noticeable the deposition of unwanted pigment particles also effects the overall quality of the color image in a detrimental manner.
It is, therefore, an object of this invention to provide an electrophoretic imaging system which will overcome the above noted disadvantages.
It is a further object of this invention to provide a photoelectrophoretic imaging process capable of producing high quality images.
It is another object of this invention to provide a novel photoelectrophoretic imaging process.
Yet still a further object of this invention is to provide a novel photoelectrophoretic imaging apparatus.
It is still a further object of this invention to provide a high contrast imaging system.